Generally, different types of reference signals are used in a communications system, where one type of reference signal is used for channel estimation, by which coherent demodulation is performed on a received signal including control information or data, and another type of reference signal is used for channel state or channel quality measurement, by which scheduling for user equipment (UE) is implemented. In a 3rd generation partnership project (3GPP) long term evolution (LTE) release 10 (R10) downlink system, a reference signal used for coherent demodulation is referred to as a demodulation reference signal (DMRS), and a reference signal used for channel state information measurement is referred to as a channel state information reference signal (CSI-RS). In addition, reference signals also include a cell-specific reference signal (CRS) inherited from an R8/R9 system, where the CRS is used for UE channel estimation, which implements demodulation of a physical downlink control channel (PDCCH) and other public channels.
In an LTE system, maximum quantities of antenna ports supported by the foregoing several types of reference signals are different. In LTE R10, the DMRS supports a maximum of eight antenna ports; in LTE R10, the CSI-RS supports a maximum of eight antenna ports, where a quantity of antenna ports may be 1, 2, 4, or 8; and in LTE R8 to R10, the CRS supports a maximum of four antenna ports, where a quantity of antenna ports may be 1, 2, or 4. In LTE R10, the DMRS supports a maximum of eight antenna ports, where a quantity of antenna ports may be 1 to 8. To improve spectral efficiency, the soon-to-be-launched LTE R12 standard has begun to consider introducing more antenna configurations, especially an antenna configuration of more than eight antenna ports based on an active antenna system (AAS). For example, a quantity of antenna ports may be 16, 32, or 64.
The prior art has at least the following problems: the prior-art CRS supports a maximum of four antenna ports, and direct expansion to support 16 antenna ports or more antenna ports may result in high overheads. The prior-art CSI-RS supports a maximum of eight antenna ports, and direct expansion in a PDSCH region to support 16 antenna ports or more antenna ports may result in interference to downlink data transmission of an existing system, causing performance degradation of a downlink system. If expansion is performed by using a neighboring resource block, correct CSI estimation cannot be performed by legacy UE. Therefore, no prior-art reference signal design solution can provide effective support for more antenna ports.